There is a great deal of research aimed at better understanding transitions in alcohol and drug (AOD) use patterns across early to late adolescence; however, there are few published studies that: a) examine developmental trajectories for more than one substance (e.g., alcohol, marijuana and cigarettes); b) measure AOD use annually during both the middle school and high school years; and c) utilize a sample with substantial racial and ethnic diversity. This application responds to PA-11-016: Epidemiology and Prevention in Alcohol Research (R01), and advances the epidemiology of underage AOD use by comparing racial/ethnic groups on their trajectories of AOD use, identifying risk and protective factors that predict AOD use trajectories, and examining how AOD-related outcomes may differ for different AOD trajectories and youth of different races/ethnicities. The current proposal is a continuation of R01AA016577 (PI: D'Amico), CHOICE, a project that assessed AOD use in 16 middle schools in Southern California with five waves of data over three years. This study focuses on two cohorts (n=5117) taken from the larger sample, which are diverse in terms of gender (50% female) and racial/ethnic composition (54% Hispanic, 16% Asian, 9% multiethnic, 15% white, and 4% Black) and follows them from 6th grade to post high school with annual assessments. Our aims are: Aim 1. Examine AOD use trajectories as youth transition from early to late adolescence. Aim 1a. Examine similarities/differences in AOD use trajectories across racial/ethnic groups. Aim 2. Examine how individual factors (e.g., expectancies, educational aspirations), family factors (e.g., family substance use, cultural values), peer factors (e.g., perceived peer use, peer approval), school factors (e.g., school-level sociodemographic composition and climate), and neighborhood factors (e.g., alcohol outlet density, SES) are associated with AOD use trajectories over time. Aim 2a. Examine similarities and differences in how these factors affect AOD trajectories across racial/ethnic groups. Aim 3. Examine the association of these AOD use trajectories with late adolescent outcomes in five key domains: academic achievement, delinquency, mental health, physical health and social functioning. Aim 3a. Examine similarities and differences in how AOD trajectories are associated with late adolescent outcomes in these five domains across racial/ethnic groups. The current study is innovative as there is little trajectory research that conducts annual assessments from early adolescence to late adolescence and assesses use across several different substances, such as alcohol, marijuana and cigarette use. Findings will significantly improve scientific knowledge in this area as they will lead to a greater understanding of racial/ethnic differences in AOD use during early to late adolescence, which could then lead to improved preventative interventions for this age group.